1. Field of Invention
The invention relates to an apparatus and method for perfusing one or more organs to monitor, sustain and/or restore the viability of the organ(s) and/or for transporting and/or storing the organ(s).
2. Description of Related Art
Preservation of organs by machine perfusion has been accomplished at hypothermic temperatures with or without computer control with crystalloid perfusates and without oxygenation. See, for example, U.S. Pat. Nos. 5,149,321, 5,395,314, 5,584,804, 5,709,654 and 5,752,929 and U.S. patent application Ser. No. 08/484,601 to Klatz et al., which are hereby incorporated by reference. Hypothermic temperatures provide a decrease in organ metabolism, lower the energy requirements, delay the depletion of high energy phosphate reserves and accumulation of lactic acid and retard the morphological and functional deterioration associated with disruption of blood supply. Oxygen can not be utilized efficiently by mitochondria below approximately 20° C. to produce energy and the reduction in catalase/superoxide dismutase production and ascorbyl and glutathione regeneration at low temperatures allows high free radical formation. The removal of oxygen from perfusates during low temperature machine perfusion has even proven helpful in improving organ transplant results by some investigators.
Reduction in potential oxygen damage is also accomplished via the addition of antioxidants to the perfusate. In particular, this has proven useful in reducing organ damage after long warm ischemia times. Numerous other perfusate additives have also been reported to improve the outcome of machine perfusion.
Ideally organs would be procured in a manner which limits their warm ischemia time to essentially zero. Unfortunately, in reality, many organs, especially from non-beating heart donors, are procured after extended warm ischemia time periods (i.e. 45 minutes or more). The machine perfusion of these organs at low temperature has demonstrated significant improvement (Transpl Int 1996 Daemen). Further, prior art teaches that the low temperature machine perfusion of organs is preferred at low pressures (Transpl. Int 1996 Yland) with roller or diaphragm pumps delivering the perfusate at a controlled pressure. Numerous control circuits and pumping configurations have been utilized to achieve this objective and to machine perfuse organs in general. See, for example, U.S. Pat. Nos. 5,338,662 and 5,494,822 to Sadri; U.S. Pat. No. 4,745,759 to Bauer et al.; U.S. Pat. Nos. 5,217,860 and 5,472,876 to Fahy et al.; U.S. Pat. No. 5,051,352 to Martindale et al.; U.S. Pat. No. 3,995,444 to Clark et al.; U.S. Pat. No. 4,629,686 to Gruenberg; U.S. Pat. Nos. 3,738,914 and 3,892,628 to Thorne et al.; U.S. Pat. Nos. 5,285,657 and 5,476,763 to Bacchi et al.; U.S. Pat. No. 5,157,930 to McGhee et al.; and U.S. Pat. No. 5,141,847 to Sugimachi et al. However, the use of such pumps for machine perfusion of organs increases the risk of overpressurization of the organ should the organ perfusion apparatus malfunction. High pressure perfusion (e.g., above about 60 mm Hg) can wash off the vascular endothelial lining of the organ and in general damages organ tissue, in particular at hypothermic temperatures where the organ does not have the neurological or endocrinal connections to protect itself by dilating its vasculature under high pressure.
Furthermore, the techniques used for assessment of the viability of these machine perfused organs have been a critical factor in limiting the organs from greater use. While increased organ resistance (i.e., pressure/flow) measurements during machine perfusion are a useful indicator, they demonstrate only the worst case situations.
During the low temperature machine perfusion of organs which have been damaged by warm ischemia time or by the machine perfusion itself, the organs will elute intracellular and endothelial as well as membrane constituents. Over the years the appearance of various ubiquitous intracellular enzymes, such as lactic dehydrogenase (LDH) and alkaline phosphatase, in the perfusate has been used as a biomarker of organ damage. Recently, the determination of the presence of alpha glutathione-S-transferase (a-GST) and Pi glutathione-S-transferase (p-GST) in low temperature machine perfusion perfusates has proven a satisfactory indicator in predicting the functional outcome of non-beating heart donor kidney grafts before transplantation (Transpl 1997 Daemen).
The prior art has also addressed the need to restore or maintain an organ's physiological function after preservation for an extended period of time at hypothermic temperatures. In particular, U.S. Pat. No. 5,066,578 to Wikman-Coffelt discloses an organ preservation solution that contains large amounts of pyruvate. Wikman-Coffelt teaches that flooding of the organ with pyruvate bypasses glycosis, the step in the cell energy cycle that utilizes adenosine triphosphate (ATP) to produce pyruvate, and pyruvate is then available to the mitochondria for oxidative phosphorylation producing ATP. Wikman-Coffelt teaches perfusing or washing an organ at a warm temperature with a first preservation solution containing pyruvate for removal of blood or other debris from the organ's vessels and to vasodilate, increase flow and load the cells with an energy supply in the form of a clean substrate, namely the pyruvate. Wikman-Coffelt teaches that the pyruvate prevents edema, ischemia, calcium overload and acidosis as well as helps preserve the action potential across the cell membrane. The organ is then perfused with a second perfusion solution containing pyruvate and a small percentage of ethanol in order to stop the organ from working, vasodilate the blood vessels allowing for full vascular flow, continue to load the cells with pyruvate and preserve the energy state of the organ. Finally the organ is stored in a large volume of the first solution for 24 hours or longer at temperatures between 4° C. and 10° C.
However, the mitochondria are the source of energy in cells and need significant amounts of oxygen to function. Organs naturally have significant pyruvate levels, and providing an organ with additional pyruvate will not assist in restoring and/or maintaining an organ's full physiological function if the mitochondria are not provided with sufficient oxygen to function. Further, briefly flooding an organ with pyruvate may, in fact, facilitate tearing off of the vascular endothelial lining of the organ.
U.S. Pat. No. 5,599,659 to Brasile et al. also discloses a preservation solution for warm preservation of tissues, explants, organs and endothelial cells. Brasile et al. teach disadvantages of cold organ storage, and proposed warm preservation technology as an alternative. Brasile et al. teach that the solution has an enhanced ability to serve as a medium for the culture of vascular endothelium of tissue, and as a solution for organs for transplantation using a warm preservation technology because it is supplemented with serum albumin as a source of protein and colloid; trace elements to potentiate viability and cellular function; pyruvate and adenosine for oxidative phosphorylation support; transferrin as an attachment factor; insulin and sugars for metabolic support and glutathione to scavenge toxic free radicals as well as a source of impermeant; cyclodextrin as a source of impermeant, scavenger, and potentiator of cell attachment and growth factors; a high Mg++ concentration for microvessel metabolism support; mucopolysaccharides, comprising primarily chondroitin sulfates and heparin sulfates, for growth factor potentiation and hemostasis; and ENDO GRO™ as a source of cooloid, impermeant and specific vascular growth promoters. Brasile et al. further teach warm perfusing an organ for up to 12 hours at 30° C., or merely storing the organ at temperatures of 25° C. in the preservation solution.
However, flooding an organ with such chemicals is insufficient to arrest or repair ischemic injury where the mitochondria are not provided with sufficient oxygen to function to produce energy. The oxygen needs of an organ at more than 20° C. are substantial and cannot be met by a simple crystalloid at reasonable flows. Further, assessment of the viability of an organ is necessary before the use of any type of solution can be determined to have been fruitful.